"I ask that the kidnappers have a sense of humanity. I beg them to return the people that they are holding to their families," he said in his weekly address to pilgrims gathered in St Peter's Square.
"I am particularly close in my thoughts and prayers to the families of those fearing for the fate of their loved ones, especially those who have been taken hostage," the 83-year pope said in a wavering voice.
More than 40 foreigners have been taken hostage in Iraq since the start of the month. Many have been released, but one group is still holding three Italian security guards captive.
A fourth Italian hostage was shot dead by the same group on Wednesday.
"I am following with great sadness the tragic news that is coming out of the Holy Land and Iraq. End this blood-letting amongst brothers. Such inhuman acts are against the will of God," the pope said.
His reference to the holy land came the day after Israel killed Hamas leader Abd Al-Aziz al-Rantisi and after a bomber killed himself and an Israeli soldier in northern Gaza.